The present invention concerns a method for determining the covering on a road surface.
The invention further concerns an apparatus for carrying out the method.
The method and the apparatus are used in order to determine any covering on a road surface and to observe the changes taking place therein in order to predict a possible slippery condition. For the road maintenance personnel, the most essential matter is to obtain a reliable estimate of freezing of the road surface preferably about two hours before freezing.
Earlier systems of warning about slippery conditions are based on measurement of moisture or water on the road surface by means of an electric conductivity detector as well as on simultaneous observation of the temperature. If the temperature is decreasing and goes below a present limit, the system alarms (e.g., Malling Kontrol, Stamholmen 173, DK-2650 Hvidovre). In more advanced systems of detectors of slipperiness, cooled and heated conductivity detectors are used, whereat the effect of salt content on the decreasing of the freezing point is taken into account (e.g., Boschung Mecatronic Ltd., CH-3185 Schmitten, Switzerland, and Findlay, Irvine Ltd., Penicuik Midlothian, Scotland EH26 9BU). Moreover, slipperiness detectors based on direct detection of ice are in use.
The most important drawback of the detectors based on electric conductivity of the road surface is that a mere conductivity reading alone cannot give information on the quantity of moisture or water on the road surface unless the salt concentration is known. On the other hand, it is difficult to distinguish between a drying road surface and a freezing road surface.
Heated and cooled conductivity detectors must be insulated thermally from the road at least partly, whereby they do not necessarily follow the temperature of the road surface reliably in all situations. Moreover, drying of the indicator detectors at different times causes situations of error.
The detectors based on direct detection of ice have a construction that poorly withstands road wear. An example is the SCAN detector of Surface Systems Inc., by means of which it is possible to distinguish between a dry, wet and icy state by the capacitance. The electrodes of the detector are protected by an epoxy layer of about 6 mm, which is worn too rapidly, at least in areas where studded tires are used.
The object of the present invention is to eliminate the drawbacks present in the prior-art technology described above and to provide a method of an entirely new type for determining any covering on road surfaces.